Shielded extensible and retractable electric conductors



Sept. 25, 1956 J. H. INGMANSON SHIELDED EXTENSIBLE AND RETRACTABLE ELECTRIC CONDUCTORS Original Filed Dec. 1, 1948 fli orneyir United States Patent SHIELDED EXTENSIBLE AND RETRACTABLE ELECTRIC CONDUCTORS Continuation of application Serial No. 62,834, December 1, 1948. This application January 5, 1952, Serial No. 265,160

3 Claims. (Cl. 17469) The present invention relates to improvements in extensible and retractable coiled electric conductors, sometimes called retractile conductors or cords, and it relates more particularly to shielded conductors of that character. Extensible and retractable electric conductors are made in helical form and are extensible against the inherent elastic resistance of the structure to the axial separation of its convolutions and are self-retracting by the elastic forces stored in the structure which tend to compact the convolutions toward each other.

For shielding on insulated wires, it has for many years been usual to employ a metallic braid of fine bare or tinned copper conductors. This well known practice was adequate for production of satisfactory shielded eelctric conductors that are straight or relatively so. However, with the advent and increasing use of extensible and retractable, or retractile, cord conductors of the type disclosed in the patent to Campbell No. 2,173,096, granted September 19, 1939, there arose a demand for shielded cord conductors of this retractile type. Attempts to meet this need by using the conventional shielding means resulted in failure. The coiled cord produced using metallic braid shielding, for example, possessed no retractile proper-ties, or at least to only a quite insutficient degree. This was found to be due to the stiffness imparted to the coiled conductor structure as a whole by a the shielding means. Moreover, it was found that obtaining effective shielding :without at the same time seriously interfering with the retractile properties of such a coiled cord was a problem not easily solved in a practical manner.

It is accordingly a principal object of the present in- Vention, heretofore unattained in the art, to provide an elfectively shielded extensible and retractable shielded electric conductor having its elements so constructed and arranged, however, that its shielding-means does not materially interfere with the desired extensibility and retractability or spring-like action of the coiled conductor structure.

Another object of the present invention, also heretoore unattained, is to provide an electric conductor of the character referred to andv having its elements so constructed and arranged that its shielding-means does not become so set in either the extended or retracted position of'it's convolutions as to materially interfere with the aforesaid spring-like action of the coiled conductor structure.

\ In order to make clear the underlying principles of the invention, a typical embodiment thereof in especially advantageous practical form will be hereinafter described in detail, and is illustrated in the accompanying drawings wherein:

Fig. 1 is a View in side elevation of a shielded extensible and retractable coiled electric conductor embodying the present invention and shown by full lines in its normal or retracted condition and shown by broken lines temporarily stretched into extended position;

Fig. 2 is a view in side elevation of a fragment of the coiled electric conductor structure of Fig. 1, with various layers thereof stripped back for clarity of illustration but on a larger scale than the showing of Fig. 1;

Fig. 3 is a transverse sectional view taken on the line 33 of Fig. 1 but on a larger scale;

Fig. 4 is a transverse sectional view taken on the line 44 of Fig. 2 but on a greatly enlarged scale;

Fig. 5 is a view in side elevation of a fragment of composite shielding cord suitable for use in carrying out the present invention; and

Fig. 6 is an enlarged-scale sectional view taken on the line 66 of Fig. 5.

So far as concerns its external form and appearance, as well as its general properties of elastic extensibility and retractability, the shielded coiled electric conductor of the present invention, as seen in Fig. 1, superficially resembles the unshielded retractile coiled conductors so long known and widely used as telephone extension cords as well as for other purposes. The retention of those highly desirable retractile properties, substantially undiminished, in the novel coiled conductor structure, despite the inclusion in said structure of metallic means operative to shield effectively the main conductor or conductors, is accomplished according to the present invention by employing shielding means of such character and so disposed with relation to the main conductor means on the one hand and, on the other, to the helical convolutions of the retractile shielded coiled conductor structure as a whole that the interference with or destruction of the desired retractile properties of the coil, formerly encountered when it was attempted to incorporate therein shielding means for the main conductor, is entirely avoided or substantially so.

Referring to the form of the invention illustrated in the drawings, the retractile shielded electrical conductor structure is shown in Fig. 1 to comprise a plurality of helical turns or convolutions 10 forming a coil of uniform diameter, from whose opposite ends extend, approximately tangentially, substantially straight terminal portions 11 and 12, respectively, of the coiled conductor. As here shown, said conductor includes an outer insulating and retractor sheath or jacket 13, directly beneath which is a binding layer 14 which envelops the main conductor means comprising at least one flexible wire insulated and shielded as will now be described in detail.

In the present instance said main conductor means is constituted by three (although there may be more or less than three) multiple-strand electric wires 15, 16, and 17', electrically insulated from each other and each, in turn, composed of a plurality of fine metal wires or tinsel to afford maximum flexibility. Each of the said electric wires is enveloped by an inner insulating sheath 18.

The respective insulating sheaths 18 of the electric wires 15 and 16 are, in turn, helically wrapped with flexible linear secondary conductor means to provide each of them with a shielding layer which is designated generally by the reference character 19 in Figs. 2, 3 and 4, and will presently be described in detail.

In a manner common in the art, groups of textile filler-strands 20 are arranged in what would otherwise be voids between the grouped wires 15, 16 and 17 (considered in conjunction with their respective laterally enveloping layers) to provide a substantially circular crosssectional form around which the binding layer 14 and outer insulating sheath 13 extend, as shown in Fig. 3.

In the particularly desirable specific embodiment of the invention here illustrated, each of the shielding layers 19 before referred to comprises flexible linear secondary conductor means provided in this instance by a plurality of composite shielding cords each generally designated by the reference character 21. Moreover, each of the said shielding layers 19 is preferably formed by simultaneously Wrapping around the given inner insulating sheath 13, helically and in contact with each other as shown, a plurality of said composite shielding cords 21 so that the pitch of the said shielding cords will be greater than would be the case were but a single shielding cord to be employed. Even as many as about sixteen shielding cords 21 may be simultaneously wrapped about a given insulating sheath. Each composite shielding cord 21 comprises in this instance a core of textile material 22 and two (more or less) relatively wide and thin metallic ribbons 23 helically wrapped around the said core in contact with each other as is clearly shown in Fig. 5. The shielding layer 19 thus produced ally in the form of a continuous yet flexible cylindrical sleeve, as is apparent.

The insulating sheaths 13 and 18 may be formed of rubber, synthetic resins or other suitable elastic insulating material, while the elements 14, 2t and 22 may be conveniently formed of cotton, silk or other nonmetallic textile material. The elements 15, 16, 17 and 23 may be formed of copper or other suitable low-resistance metals.

As the elements 13 to 23 are thus constructed and arranged, the metallic ribbons 23 form relatively minute helices throughout the relatively major helix ill of the entire structure as illustrated in Fig. 1, with the result that the helices 10 may be separated from each other in extending the electric conductor and may return to normal and substantially abutting positions, as indicated in Fig. 1, without the said minute helices exerting appreciable resistance to the said extension and contraction. it should be noted that this efleot is also furthered by the fact that the helices in which the composite shielding cords 21 are wrapped about the underlying insulating sheaths 18 are also very much smaller than the aforesaid relatively major helices 10 of the coiled conductor structure as a whole.

Furthermore, by virtue of the construction and arrangement of the elements above described, the metallic ribbons 23 do not become so distorted from their normal helical path when the structure is either fully stretched or fully contracted, as to become set.

The extensible and retractable electric conductor in the form illustrated in Fig. 1 may be produced in accordance with the usual practice well known in the art, by wrapping a conductor embodying the features 13 to 23 inclusive helically around a mandrel with the respective opposite ends of the coil left substantially straight to provide the terminal ends 11 and 12. The mandrel together with the helically wrapped conductor may then be subjected to a heating operation to set the external insulating and retractor sheath 13 in helical form. It is the usual practice, after the structure has become cool, to reverse the direction of the helices in order to make the contractive tension of the structure more pronounced.

The invention may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

is virtu- This application is a continuation of my prior copending application Serial No. 62,834, filed December 1, 1948, now abandoned.

I claim:

1. A shielded electric conductor having a coiled main conductor portion consisting substantially of a series of coiled convolutions of said conductor portion, said coiled convolutions normally being adjacent one another in retracted relation, and being spreadable apart to extended relation, and said coiled conductor portion comprising in combination: a flexible electric wire extending along the interior of and as part of said coiled conductor portion; a flexible insulating sheath extending along the interior of and as part of said coiled conductor-portion and enveloping said electric wire; a shielding layer extending along the interior of and as part of said coiled conductor portion and enveloping said flexible wire and said inner insulating sheath, and comprising at least one composite shielding cord extending helically around said insulating sheath, each said composite shielding cord consisting substantially of a flexible textile core and at least one relatively wide and thin flat metallic ribbon extending fiatwise helically around said textile core; and an elastic retractor sheath extending along and as part of said coiled conductor portion and enveloping said flexible wire and said insulating sheath and said shielding layer, and elastically resisting spreading apart movement of said coiled convolutions toward their extended relation, and elastically urging said coiled convolutions from their extended relation toward their retracted relation.

2. In a retractile shielded electrical conductor structure having the form of an extensible, self-retracting helical coil, the combination comprising a main conductor portion including at least one flexible electric wire which is sheathed in flexible insulating material and extends along the interior of and as part of the coiled conductor structure, and a flexible shielding layer encasing the insulated main conductor portion and formed by flexible linear secondary conductor means helically wrapped about and encasing the same, said secondary conductor means being in the form of composite cord comprising a flexible core with at least one thin flexible low-resistance metal conductor helically wrapped about and encasing said core, together with a flexible elastic outer sheath of insulating material, set in helical form, enveloping the foregoing main and secondary conductor assemblage, which sheath elastically resists axial separation of the convolutions of the complete coiled structure and normally maintains them in retracted relation; the helical convolutions of the metal wrapping in said flexible secondary conductor means being relatively minute as compared to those of the shielded conductor as a whole.

3. The retractile shielded electrical conductor structure defined by claim 2, wherein said shielding layer comprises a plurality of such composite cords simul taneously wrapped helically about said insulated main conductor portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,573,439 Henning Oct. 30, 1951 FOREIGN PATENTS 649,029 Germany Aug. 13, 1937 

